Annual Pollution Report

Transcription

1 Annual Pollution Report to the Legislature March 2006 ~ Minnesota Pollution Control Agency %;:l;--r

2 Tom Clark, Patricia Engelking and Kari Palmer of the Water Assessment and Environmental Information Section of the Environmental Analysis and Outcomes Division prepared this report, with assistance from other staff in the Municipal, Industrial, Regional, and the Environmental Analysis and Outcomes divisions. Cost to prepare this report: Total staff hours: hours Salary and fringe costs: $6396 Production costs: $216 An electronic version of this report can be found on the MPCA web site at This report can be made available in other formats, including Braille, large type, or audiotape upon request. This report is printed on paper with at least 30 percent post-consumer recycled paper.

3 Table of Contents List of Tables and Figures... ii Foreword... iii Introduction and Summary...1 Chapter 1: Air Pollutant Emissions Overview...5 Criteria Air Pollutant Emissions...6 Air Quality Index (AQI)...8 Particulate Matter...10 Ozone...16 Nitrogen Oxides...17 Volatile Organic Compounds...19 Carbon Monoxide...21 Sulfur Dioxide...23 Lead...25 Carbon Dioxide...27 Mercury...29 Air Toxics...31 Chapter 2: Water Pollutant Discharges Overview...40 Major Water Discharge Parameters and Trends...41 Total Suspended Solids...41 Biochemical Oxygen Demand (BOD) and Carbonaceous BOD...42 Total Phosphorus...43 Nitrogen...44 Nonpoint Source Pollution...45 Other Contaminants of Concern in Minnesota...48 lrp-ear-2sy06

4 List of Tables Table 1: Minnesota Air Pollution Emission Estimates, Table 2: Minnesota Water Pollution Discharge Estimates from Major Point Sources, Table 3: 2002 Minnesota Air Toxics Emissions Inventory Statewide Summary...32 List of Figures AQI Days for Selected Cities in Minnesota, Sources of Fine Particulate (PM 2.5 ) Emissions in Minnesota, PM 2.5 Composition at Three Minnesota Sites, October 2001-September Sources of PM 10 Emissions in Minnesota, PM 10 Point Source Emission Trends by Sector in Minnesota, Sources of Nitrogen Oxide Emissions in Minnesota, Nitrogen Oxide Point Source Emission Trends by Sector in Minnesota, Sources of Volatile Organic Compounds in Minnesota, Volatile Organic Compound Point Source Emission Trends by Sector in Minnesota, Sources of Carbon Monoxide Emissions in Minnesota, Carbon Monoxide Point Source Emissions Trends by Sector in Minnesota, Sources of Sulfur Dioxide Emissions in Minnesota, Sulfur Dioxide Point Source Emission Trends by Sector in Minnesota, Sources of Lead Emissions in Minnesota, Lead Point Source Emission Trends by Sector in Minnesota, Sources of Carbon Dioxide Emissions from Fossil Fuel Burning in Minnesota, Carbon Dioxide Emission Trends from Fossil Fuel Burning in Minnesota, Sources of Atmospheric Mercury Deposition to Minnesota...29 Trends in Minnesota Mercury Emissions from Human Activities, Contribution of Principal Source Categories to 2002 Air Toxics Emissions in Minnesota...36 Contribution of Major Categories to 2002 Point Source Air Toxics Emissions in Minnesota...37 Contribution of Major Categories to 2002 Area Source Air Toxics Emissions in Minnesota...38 Contribution of Major Categories to 2002 Mobile Source Air Toxics Emissions in Minnesota...39 Total Suspended Solids Discharges from Major Point Sources, Biological Oxygen Demand Discharges from Major Point Sources, Total Phosphorus Discharges from Major Point Sources, Ammonia Discharges from Major Point Sources, ii

5 Foreword The Annual Pollution Report statute requires the Minnesota Pollution Control Agency (MPCA) to estimate to the best of its ability the total amounts of air and water pollution emitted in the state during the most recent calendar year for which data are available. The statute further directs the MPCA to estimate the percentage increase or decrease over the previous calendar year, and to estimate the relative contributions of the various sources of these emissions and discharges to the environment. The MPCA has prepared this report since It has evolved to include new kinds of information, such as discharges of toxic air pollutants, greenhouse gas emissions, and emerging contaminants of concern as these kinds of data have become available. The following observations of some strengths and shortcomings of the current reporting process are presented for interested parties to help determine if and how the report should be changed. Strengths The Annual Pollution Report is the only MPCA report that specifically asks for an accounting of emissions and discharges. Such inventories are inherently important, as understanding emission amounts and sources is fundamental in protecting the environment and human health. The report attempts to track trends year to year, which is valuable if data are reliable. The report covers both air and water pollutants in one document, instead of separate reports, reminding readers of the potential for cross-media impacts. The report shows relative contributions of various pollution sources to the total. Minn. Statutes Annual pollution report. A goal of the pollution control agency is to reduce the amount of pollution that is emitted in the state. By April 1 of each year, the pollution control agency shall report the best estimate of the agency of the total volume of water and air pollution that was emitted in the state in the previous calendar year for which data are available. The agency shall report its findings for both water and air pollution: (1) in gross amounts, including the percentage increase or decrease over the previous calendar year; and (2) in a manner which will demonstrate the magnitude of the various sources of water and air pollution. HIST: 1995 c 247 art 1 s 36; 2001 c 187 s 3 Copyright 2001 by the Office of Revisor of Statutes, State of Minnesota. Shortcomings Aggregating data into total volumes lacks the important context of relative risk. Pollutants emitted in smaller volumes can have a greater impact than some emitted in tremendously larger volumes. The volume figures also do not convey whether such emissions and discharges are acceptable or unacceptable from a risk perspective. The most current pollutant emissions and discharge data are usually at least two years behind real time, sometimes more, depending on the type of pollutants. Air emission estimates are frequently revised as industrial output models and factors used to estimate emissions are refined. Year-to-year comparisons are not always reliable, as methodologies for estimating emissions are still evolving. iii

6 Shortcomings, cont. There is currently no reliable way to quantify the volumes of water pollutants released by nonpoint sources in the form of polluted runoff, such as city streets, construction sites and farm fields. This is a major gap in inventorying pollutants discharged, for a category highly culpable for water quality impairments. As with the 2005 report, this year s report presents some of the information differently. For example: Air pollution estimates for point source emissions are based on the Minnesota emission inventory. Nonpoint source water pollutant estimates are being highlighted in basin-loading studies, which attempt to quantify the amounts of specific pollutants entering a given watershed from specific sources, both point and nonpoint. While this falls short of being able to quantify nonpoint source discharges statewide, it represents an important first step to better understanding the relative contributions of point and nonpoint sources to specific watersheds, which in turn can guide local and state officials in planning for water quality improvements. The examples noted above are presented to help the reader get a sense for the dilemmas the MPCA faces in attempting to deliver accurate, timely and useful information about what is discharged into Minnesota s air and water. The MPCA has significantly expanded and improved public access to environmental data available electronically through its Environmental Data Access Initiative, funded by the Legislature. Water quality data and air quality data from all over the state are now easily available at this link: As this system continues to grow and evolve, the MPCA will evaluate new reporting formats for presenting annual pollution data. The agency welcomes suggestions from interested parties for upgrading the current reporting process to better meet the purpose envisioned in the statute. iv

7 Introduction and Summary The Minnesota Pollution Control Agency (MPCA) is required by Minnesota Statutes, Chapter to submit to the Legislature an annual report of the volume of pollution emitted or discharged to the state's air and water resources. In addition to gross amounts, the MPCA must report the annual percentage increase or decrease of pollutants for the most recent year for which data are available. The report must also demonstrate the magnitude of the various sources of air and water pollution. The basis of the MPCA's 2006 Annual Pollution Report is the 2002 and 2004 Minnesota Criteria Pollutant Emission Inventories, the 2002 Air Toxics Emission Inventory and the 2004 Water Quality National Pollutant Discharge Elimination System (NPDES) Discharge Monitoring Reports. Annual emission and discharge estimates are one important component of tracking progress on air and water pollution, and for tracking performance and relative contributions of pollution sources. The MPCA also regularly prepares reports on the physical, chemical and biological conditions measured in the environment, and on pollutants of special concern to human health and the environment. These reports and others are available on the Internet and are referenced throughout this document for readers who would like additional context and information. Air Emissions The MPCA reports data from its own Minnesota Criteria Pollutant Emission Inventory, using data generated in the state. Prior to the 2004 report, EPA data was used. The major air pollutants summarized in this report include carbon monoxide (CO), nitrogen oxides (NO x ), sulfur dioxide (SO 2 ), volatile organic compounds (VOCs), particulate matter (PM 10 and PM 2.5 ) and lead. These are known as the criteria pollutants. The most recent emissions data available from large facilities for these pollutants are from About Emission Inventories Completing air pollutant emission inventories is a time-intensive process. For example, to develop the point source part of the Criteria Pollutant Emission Inventory for the year 2004, facilities with MPCA permits had until April 1, 2005 to submit their 2004 emissions estimates to the MPCA. Agency staff then compiled these emission estimates into a draft Criteria Pollutant Emission Inventory, which was sent back to the facilities for review in October Facilities completed their review by November, MPCA staff then reviewed the changes and completed the inventory for 2004 in January The Minnesota Air Toxics Emission Inventory and the area and mobile source components of the Criteria Pollutant Emission Inventory are completed once every three years to coincide with the three-year cycle of the U.S. EPA's National Emission Inventory. MPCA staff develop emissions estimates for the Air Toxics Emission Inventory based upon the completed Criteria Pollutant Emission Inventory, the assistance of permittees, and available information from other state and federal agencies. Global climate change is a continuing concern worldwide. Therefore, Minnesota emissions of the principal greenhouse gas, carbon dioxide (CO 2 ), are included for The statewide emissions were calculated using a variety of fuel use data sources. 1

8 The Minnesota Air Toxics Emission Inventory estimates emissions of air toxics including compounds such as benzene and formaldehyde. There is some overlap between the Minnesota Air Toxics Emission Inventory and the estimates for VOCs because many air toxics are also VOCs. The most recent inventory of air toxics emissions is from Table 1 lists the total statewide emissions of the major air pollutants from 2000 to The percent change from 2003 to 2004 is given in the final column. It is possible to look at emission trends between these years. However, it is important not to place undue emphasis on a yearly change. Trends should be viewed over several years of data. In addition, emission estimates fluctuate as a result of changes and improvements in the inventory. The MPCA releases a complete emission inventory including criteria pollutants and air toxics every three years. Emissions of criteria pollutants from large facilities are estimated every year. Therefore, the 2004 emissions include 2004 criteria emissions from large facilities. The numbers include 1999 data from smaller area and mobile sources. Updated 2002 emissions from area and mobile sources are used for Table 1: Minnesota Air Pollution Emission Estimates, (thousand tons)* Pollutant % Change Carbon monoxide (CO) % Sulfur dioxide (SO 2 ) % Oxides of nitrogen (NO x ) % Volatile organic compounds % (VOCs) Particulate matter (PM 10 )** % Total % *1999 mobile and area emission estimates are used in Preliminary 2002 mobile and area emission estimates were used in **PM 10 emissions represent only primary formation; secondary formation is not included. There may be differences in the total emission figures for a given year discussed in this report versus emission reports that the MPCA has published prior to 2004 because MPCA data are being used instead of EPA data. Differences in methodology exist between the two inventories. In addition, data may be updated in MPCA s emission inventory due to corrections or changes in methodology. It should also be noted that despite the importance of the secondary formation of particulate matter, estimated air emissions data in this report are only based on direct releases from sources into the atmosphere. Secondary formation occurs when emissions of volatile gases combine and form fine particles. These particles are not directly emitted but are formed downwind of the emission source. Although EPA-approved models to predict the secondary formation of fine particles do not currently exist, work is underway to develop these models. Direct emissions of fine particles (PM 2.5 ) from all categories are included for the first time this year in the Minnesota Criteria Pollutant Emission Inventory. PM 2.5 is not included in Table 1 since PM 2.5 emissions are a subset of the PM 10 emissions. Most pollutant emission estimates were unchanged between 2003 and Only sulfur dioxide decreased by nearly four percent due primarily to an estimated decrease in emissions from utilities. A similar increase in sulfur dioxide from utilities was seen in Many air toxics are also VOCs. To avoid double-counting, the preliminary 2002 air toxics emissions are given in the body of the report. 2

9 Water Discharges Summary Owners or operators of any disposal system or point source are required by Minnesota Statutes, Chapter (7) to maintain records and make reports of any discharges to waters of the state. These selfmonitoring reports submitted to MPCA are commonly referred to as Discharge Monitoring Reports. These data, which can be generated from either the EPA s Permit Compliance Tracking System (PCS) or the MPCA's DELTA database, are the basis for the point source discharge summary (Table 2). Table 2: Minnesota Water Pollution Discharge Estimates From Major Point Sources, (thousand kilograms) Pollutant to 2004 % Change Total suspended solids 5,100 8,600 7,500 5,700 4, Biochemical oxygen 3,500 4,900 4,200 3,700 3, demand (BOD) Phosphorus 1,400 1,400 1,300 1, Ammonia Nitrogen 1,300 1,000 1,100 1, (NH 3 ) Nitrate Nitrogen (NO 3 ) 4,700 4,300 4,200 3,100 3, Total 16,000 20,200 21,300 15,400 12, In Table 2, discharge estimates for were generated from PCS, while data for were generated from DELTA. The reported 2002 values represent the previously reported statewide totals calculated by PCS, adjusted by substituting a few values from DELTA. Data for years prior to 2002 have not been examined in any detail using DELTA. The MPCA began using DELTA to generate the reports on which this section is based when inconsistencies in EPA s Compliance Tracking System database were noted, beginning with the 2003 data summary. Using DELTA allows uniform assumptions about loading to be made throughout MPCA's water programs. The MPCA intends to use DELTA as a basis for this and similar reports for 2003 and beyond. The MPCA s water quality program is evolving from a predominantly concentration-based, facility-byfacility regulatory approach to one that emphasizes managing total pollution discharges to Minnesota s waters. The current report represents an important step in improving the agency's capacity to accurately perform loading analyses. Due to the multi-year life of permit requirements, however, many permits do not yet contain monitoring and reporting requirements that enable efficient, computerized calculations of total pollutant loadings. As the agency re-issues permits and further assesses the data, it will continue to build capability in this area. In some cases, values calculated using DELTA vary substantially from those previously derived from PCS. One difference between the totals from PCS and those from DELTA results in the loadings calculated by PCS being greater than those calculated using DELTA. When accounting for reported values that are less than a detection limit, PCS uses 100% of the reported numerical component of the value in its calculations; in the calculations performed using DELTA for this report, 50% of the reported numerical value was used. 3

10 In addition to the specific variances and adjustments highlighted above, there are a number of additional sources of variation, both up and down, that potentially impact year-by-year comparisons: Over 30,000 individually reported values have been incorporated into the yearly totals, often in ways that are optimized for concentration-based compliance determination, not environmental assessment. The loading calculations incorporate a number of data processing decisions that can legitimately be made using a variety of methods. Reporting requirements can vary with each permit issuance, resulting in variation in parameters reported with time making year-by-year comparisons difficult. The loading calculations do not currently account for unmonitored or missing parameters and periods, so a facility that only monitors or reports quarterly on a pollutant, for example, is presumed to discharge that pollutant only in the months that were reported. Wastewater treatment facilities regularly experience variations in influent strength, influent flow and facility performance from day-to-day and year-to-year. The 2004 figures represent the combined loading from 89 major municipal and industrial discharges of more than one million gallons per day to waters of the state. These major facilities represent approximately 85% of the total volume of discharge to waters of the state from point sources. The remaining 15% comes from many smaller municipal and industrial facilities. Although discharges from these facilities are small, they can have significant impacts on individual lakes and stream segments. Of the 89 major facilities reporting in 2004, 39 showed an increase in total loading over 2003, 46 showed a decrease in total loading, and four facilities reported insufficient data to allow a determination to be made. The decrease in total loading to waters of the state (Table 2) represents a return to the year-to-year downward trend noted from before the flood year of 2001 (when the Mississippi River was above flood stage for over a month during the spring) and 2002 (a record wet year in many areas, with frequent high-intensity rainfall events). In 2003, spring snowmelt, runoff and precipitation returned to a more normal pattern, and this is one factor that may be reflected in the overall decrease in total loading for 2004, as shown by decreases in total suspended solids (TSS), biochemical oxygen demand (BOD), phosphorus (P) and ammonia nitrogen (NH 3 ) for the statewide database. Point source contributions of nitrate and phosphorus to waters of the state are still small compared to nonpoint contributions of these pollutants from sources such as agriculture and urban runoff. Point sources tend to have the greatest impact on receiving waters during periods of low precipitation and stream flow, while nonpoint sources are most significant during periods of high precipitation and stream flow. However, it is difficult to measure directly the effects of nonpoint pollution on Minnesota s lakes, rivers and ground water. Best estimates suggest that approximately 86% of water pollution in Minnesota can be attributed to nonpoint sources, while about 14% comes from point sources. The MPCA continues to investigate better ways to assess and measure nonpoint pollution, but nonpoint source monitoring is expensive and often requires a more complex, labor-intensive (and therefore more costly) monitoring network than measuring volume and quality of discharge from pipes. The MPCA continues to conduct loading studies for a number of watersheds in the state. The 2004 and 2005 Annual Pollution Reports included case histories of the Crow River basin, the Minneapolis chain of lakes, and the Shingle Creek watershed. This year's report includes a further look at the Shingle Creek watershed where best management practices (BMPs) are being implemented to reduce the impact of road salt and other deicing chemicals on waters of the state. 4

11 Chapter 1: Air Pollutant Emissions Overview Thousands of chemicals are emitted into the air. Many of these are air pollutants that can directly or indirectly affect human health, reduce visibility, cause property damage and harm the environment. For these reasons, the MPCA attempts to reduce the amount of air pollutants released into the air. In order to understand how much pollution is released and to track the success of reduction strategies, the MPCA estimates the emissions of certain air pollutants released in Minnesota. Criteria Pollutants The 1970 Clean Air Act identified six major air pollutants that were present in high concentrations throughout the United States called criteria pollutants. These air pollutants are particulate matter (PM 10 ), sulfur dioxide (SO 2 ), nitrogen oxides (NO x ), ozone (O 3 ), carbon monoxide (CO) and lead (Pb). Fine particles (PM 2.5 ) were later included as a criteria pollutant. The Minnesota Criteria Pollutant Emission Inventory estimates emissions of five criteria pollutants (PM 10, SO 2, NO x, CO and Pb). Ozone is not directly emitted, so a group of ozone precursors called volatile organic compounds (VOCs) is included instead. PM 2.5 was calculated for the first time for the 2002 emissions inventory. The Criteria Pollutant Emissions section also includes a summary of the MPCA s Air Quality Index (AQI) data for Greenhouse Gases Although greenhouse gases do not necessarily directly harm human health, their increase in concentration can lead to global climate change. The principal greenhouse gas emitted is carbon dioxide (CO 2 ). MPCA tracks CO 2 emissions in Minnesota. Air Toxics Many other chemicals are released in smaller amounts than the criteria pollutants, but are still toxic. The EPA refers to chemicals that can cause serious health and environmental hazards as hazardous air pollutants or air toxics. Air toxics include chemicals such as benzene, formaldehyde, acrolein, mercury and polycyclic organic matter. Minnesota data come from the preliminary 2002 Minnesota Air Toxics Emission Inventory. This report is limited to a summary and discussion of emissions of various air pollutants in Minnesota. However, the MPCA has prepared several other reports that discuss air pollution trends and emissions in more detail. Please reference the following reports for more information regarding air pollution. Air Quality in Minnesota: Progress and Priorities 2005 Report to the Legislative Air Quality in Minnesota: Into the Future 2003 Report to the Legislative Air Toxics Monitoring in the Twin Cities Metropolitan Area Preliminary Report 5

12 Criteria Air Pollutant Emissions Minnesota s Emission Inventory Rule requires all facilities in Minnesota that have an air emissions permit to submit an annual emission inventory report to the Minnesota Pollution Control Agency (MPCA). The report quantifies emissions of the regulated pollutants listed below: carbon monoxide (CO) nitrogen oxides (NO x ) lead (Pb) particulate matter less than 10 microns in diameter (PM 10 ) sulfur dioxide (SO 2 ) volatile organic compounds (VOC) The emission inventory is used to track the actual pollutant emissions of each facility and to determine the type and quantity of pollutants being emitted into the atmosphere. Ozone is a criteria pollutant that is not directly emitted, so a group of ozone precursors called volatile organic compounds (VOCs) is included instead. The data is then used to calculate an annual emission fee for each facility. Starting with the 2002 inventory, MPCA has also begun estimating PM 2.5 emissions. The Minnesota Criteria Pollutant Emission Inventory estimates emissions from permitted facilities every year in order to fulfill the Minnesota rule. In addition, every three years, the MPCA estimates emissions from two other principal source categories: area sources and mobile sources. Overall, the Minnesota Criteria Pollution Emission Inventory includes emissions from three principal source categories. 1. Point Sources: Typically large, stationary sources with relatively high emissions, such as electric power plants and refineries. A "major" source emits a threshold amount (or more) of at least one criteria pollutant, and must be inventoried and reported. 2. Area Sources: Typically stationary sources, but generally smaller sources of emissions than point sources. Examples include dry cleaners, gasoline service stations and residential wood combustion. Area sources may also include a diffuse stationary source, such as wildfires or agricultural tilling. These sources do not individually produce sufficient emissions to qualify as point sources. For example, a single gas station typically will not qualify as a point source, but collectively the emissions from many gas stations may be significant. 3. Mobile Sources: Mobile sources are broken up into two categories; on-road vehicles and nonroad sources. On-road vehicles include vehicles operated on highways, streets and roads. Nonroad sources are off-road vehicles and portable equipment powered by internal combustion engines. Lawn and garden equipment, construction equipment, aircraft and locomotives are examples of non-road sources. The Minnesota Criteria Pollutant Emission Inventory is complete for point sources through Emission estimates are available for area and mobile sources for When 2004 summary data is given, it includes area and mobile data from 2002 and point source data from This report presents trend data for point sources from

13 With each new inventory, improvements are made in terms of pollutants covered, source categories included, and the accuracy of emission estimates. Therefore, changes in the way emissions are calculated may affect trends, even if there was no real increase or decrease in emissions. The reader may note differences in the total emission figures for a given year discussed in this report versus previous emission reports the MPCA has published because MPCA data is used starting with the 2004 report. Prior to 2004, EPA emissions data was used. Differences in methodology exist between the two inventories. Data may be also updated in past emission inventories due to corrections or changes in methodology. In addition, despite the importance of secondary formation for some pollutants (e.g. PM 10 ), estimated air emissions data in this report are based on direct releases from sources into the atmosphere. Secondary formation of pollutants is not included in the estimates because there is currently no reliable way to estimate their quantity. However, models to predict secondary formation of particles are under development. Find more information on the Minnesota Criteria Pollutant Emission Inventory: See the MPCA Environmental Data Access web site to download MPCA emission estimates: Find more information on criteria air pollutants in the following EPA web site: See the EPA AIRData web site to download EPA criteria pollutant emission estimates: 7

14 Air Quality Index (AQI) The Air Quality Index (AQI) was developed by the EPA to provide a simple, uniform way to report daily air quality conditions. In Minnesota, four criteria pollutants are used to calculate the AQI: ground-level ozone, sulfur dioxide, carbon monoxide and fine particles (PM 2.5 ). High AQI days in Minnesota are usually the result of elevated levels of ozone and PM 2.5. The AQI is currently calculated for the Brainerd area, Detroit Lakes, Duluth, Ely, Marshall, Rochester, St. Cloud, and the Twin Cities area. All pollutants are not necessarily monitored at each location. The AQI translates each pollutant measurement to a common index, set at 100 to reflect where health effects might be expected in sensitive populations. The pollutant with the highest index value is used to determine the overall AQI. The table below shows the different AQI categories along with the corresponding index range. AQI Color Legend: Good 0-50 Moderate Unhealthy for Sensitive Groups Unhealthy Very Unhealthy The AQI in Minnesota cities rarely reaches the Unhealthy range; however, many citizens are affected by air quality in the Unhealthy for Sensitive Groups category. The chart on the next page displays the number of Good, Moderate, Unhealthy for Sensitive Groups and Unhealthy days for several cities in Minnesota that were monitored every day in Days are categorized by the highest AQI level calculated anytime during that day. The EPA may report different AQI summary totals for Minnesota because the MPCA and EPA use different methods to calculate the AQI. In 2005, the Twin Cities had 166 Good air quality days, 191 Moderate air quality days, 5 days that were considered Unhealthy for Sensitive Groups and 3 Unhealthy days. The Twin Cities area likely has the highest number of Moderate and Unhealthy for Sensitive Groups days because it has a higher population and more sources of ozone and PM 2.5 than the other regions. 8

15 AQI Days for Selected Cities in Minnesota, Days of the Year Unhealthy Unhealthy for Sensitive Groups Moderate Good Twin Cities Rochester St. Cloud Duluth References/Web Links For more information on the AQI, see the following web sites:

16 Particulate Matter Particulate matter is the general term for particles found in the air, including dust, dirt, soot, smoke, and liquid droplets. Some particles are seen as soot or smoke. Others are so small that they can only be detected with an electron microscope. Particles less than or equal to 2.5 micrometers (μm) in diameter, or PM 2.5, are known as fine particles. Those larger than 2.5 μm but less than or equal to 10 μm are known as coarse particles. PM 10 refers to all particles less than or equal to 10 μm in diameter. Both coarse and fine particles can be inhaled into the lungs. These particles then accumulate in the respiratory system and are associated with numerous adverse health effects, which are briefly described in the following sections. Particulate matter also causes adverse impacts to the environment. Fine particles are the major cause of reduced visibility in parts of the United States. In addition, when particles containing nitrogen and sulfur deposit onto land or water bodies, they may affect nutrient balances and acidity. This can result in the depletion of nutrients in the soil, damage to sensitive forests and farm crops, and diversity changes in ecosystems. Particulate matter also causes soiling and erosion damage to materials and buildings. 10

17 PM 2.5 Fine particles can be inhaled deeply into the lung. These particles then accumulate in the respiratory system and are linked to a range of serious health effects. Studies of short term peaks in PM 2.5 and/or of long term exposures have found fine particles associated with increased cardiovascular and respiratory hospital admissions, emergency room visits, and deaths; heart attacks; chronic bronchitis; reduced lung function growth and increased respiratory illness in children; asthma attacks; and lung cancer deaths. For five days in 2005, levels of fine particles were either Unhealthy or Unhealthy for Sensitive Groups in the Twin Cities area. PM 2.5 was also responsible for the majority of Moderate air quality days. The number of Moderate days is significant because EPA estimates greater overall health risks associated with the Moderate days than the relatively fewer Unhealthy or Unhealthy for Sensitive Groups days. Emissions Data and Sources The MPCA estimate for statewide direct emissions of PM 2.5 in 2002 is 181,650 tons. The figure below shows estimated sources of 2002 PM 2.5 direct emissions. Sources of Fine Particulate (PM 2.5 ) Emissions in Minnesota, 2002 Unpaved Roads 39% Non-Road 5% On-Road 2% Point 6% Area 87% Other 8% Waste Disposal, Open Burning 4% Paved Roads 4% Construction 4% Residential Wood Burning 7% Forest Wildfires 7% Agriculture Production - Crops, Tilling 27% Direct source emissions of PM 2.5 are included in the 2002 inventory. However, secondarily formed particles, which are not directly emitted but are formed downwind of the emission source, are not included because this formation cannot be accurately quantified at this time. This is significant because secondary particles are a major component of the mass of ambient PM

18 The majority of the mass of direct emissions come from soil. These sources are of less concern from a human health perspective. Fine particles released directly from combustion, for example, when coal, gasoline, diesel, other fossil fuels and wood are burned, are believed to pose greater health risks. Many particles are also formed secondarily in the atmosphere from chemical reactions involving gaseous pollutants such as nitrogen oxides, sulfur oxides, some volatile organic compounds and ammonia. Major sources of fine particles are cars, trucks, buses, diesel construction equipment, coal-fired power plants, biomass (wood, vegetation, etc.) burning and agriculture. Because they are tiny and light, fine particles can be carried by the wind for hundreds of miles, making exposure to these pollutants a regional problem. Unlike ozone, which is typically elevated in the hot summer months, fine particles can be a problem throughout the year. To further understand the sources of fine particles, the MPCA had three monitors in St. Paul, Minneapolis and Rochester set up to help determine the source of particles in urban areas. The figure below shows the results of a preliminary analysis of the major PM 2.5 components from these monitors. PM 2.5 Composition at Three Minnesota Sites, October 2001-September Concentration (ug/m3) Organic Carbon Elemental Carbon Nitrate Sulfate Ammonium Soil Other 2 0 St. Paul (Harding) Minneapolis (Phillips) Rochester The concentrations of the different fractions of PM 2.5 are very similar across the three monitors. The largest fraction is organic carbon, followed by sulfate and nitrate. Getting a sense of the composition of fine particles in Minnesota can help to pinpoint the sources of these particles. Organic carbon particles: These can be either primary particles or can be formed secondarily from the reaction of some volatile organic compounds. They can result from human activities (fossil fuel consumption, prescribed fires, cooking) or biogenic activities (vegetative material, biogenic gases, naturally occurring forest fires). Scientists are unsure at this point whether the majority of organic carbon 12

19 particles are of primary or secondary origin. See the Volatile Organic Compounds section on page 19 of this report for Minnesota s 2004 VOC emissions associated with human activities. Fine sulfate particles: These result from the oxidation of sulfur dioxide, forming sulfuric acid, which can then react with ammonia. Most sulfur dioxide emissions result from human sources including coalfired power plants and other industrial sources such as smelters, boilers and oil refineries. See the Sulfur Dioxide section on page 23 of this report for Minnesota s 2004 SO 2 emissions. Nitrate particles: These particles form from the oxidation of nitrogen oxides. Nitrogen oxide gases are released from virtually all combustion activities, especially those involving cars, trucks, buses, off-road sources (e.g., construction equipment, lawn mowers and boats), coal-fired power plants and other industrial sources. See the Nitrogen Oxides section on page 17 of this report for Minnesota s 2004 NO x emissions. Elemental carbon particles: These particles are commonly called soot. They are smaller than most particles and tend to absorb rather than scatter light. These particles are emitted into the air from virtually all combustion activity, but are especially prevalent in diesel exhaust and smoke from the burning of wood, other biomass and wastes. Ammonia: Most of the ammonia emitted in Minnesota is generated from livestock waste management and fertilizer production. The ammonia is in the form of ammonium ions in particles. Soil Fraction: This fraction consists of primary particles that are eroded from the landscape. References/Web Links For more information on PM 2.5, see the following web sites:

20 PM 10 Exposure to PM 10 particles is primarily associated with the aggravation of respiratory conditions such as asthma. PM 10 has also been linked to cardiovascular mortality and related health effects, but many studies indicate a stronger association between PM 2.5 and these health effects. PM 10 particles are generally emitted from sources such as vehicles traveling on unpaved roads, materials handling, and crushing and grinding operations, and windblown dust. These particles can settle rapidly from the atmosphere within hours, and their spatial impact is typically limited (compared to PM 2.5 ) because they tend to fall out of the air in the downwind area near their emissions point. Emissions Data and Sources The MPCA estimate for statewide direct emissions of PM 10 in 2004 is 783,466 tons. The figure below shows estimated sources of 2004 PM 10 direct emissions. Sources of PM 10 Emissions in Minnesota, 2004 Unpaved Roads 56% Non-road Sources 1% On-road Vehicles 0.5% Point 4% Area 94% Other 9% Paved Roads 6% Agriculture Production 29% Point source data is from the 2004 Emissions Inventory. All other data is from the 2002 Emissions Inventory. PM 10 particles formed secondarily in the atmosphere from chemical reactions involving gaseous pollutants such as nitrogen oxides, sulfur oxides, some volatile organic compounds and ammonia are not accounted for in these pie charts and graphs. Area sources contribute 94 percent of PM 10 emissions. The majority of area source emissions are the result of dust from unpaved roads (56 percent) and agriculture production (29 percent). Fugitive dust from paved roads and construction and combustion sources make up the remainder of the area source contribution. Point sources account for 4 percent of PM 10 emissions. These emissions come primarily from the mining, manufacturing and utility sectors. On-road vehicles and non-road mobile sources make up about 2 percent of total PM

21 Although most of the mass of PM 10 emissions come from soils carried by the wind, these sources tend to be located away from people and are often larger particles, which are less of a human health concern. Particles emitted from combustion sources such as cars, wood stoves, and industrial and commercial combustion are generally smaller, more toxic and more often released in populated areas. Trends In 2004, point sources contributed 4 percent to the total state PM 10 emissions. Emissions from the mining sector decreased significantly in This decrease in mining emissions of PM 10 was due primarily to the closing of LTV Steel Company. PM 10 emissions have been slowly increasing since 2001, which may be due to a gradual economic recovery from the 2001 recession. Emissions increased slightly between 2003 and 2004 in all sectors except utilities PM 10 Point Source Emission Trends by Sector in Minnesota, , Tons Manufacturing Utilities Mining Refineries Pulp & Paper Other References/Web Links For more information on PM 10, see the following web sites:

22 Ozone Ozone is an odorless, colorless gas composed of three atoms of oxygen. Naturally occurring ozone in the upper atmosphere helps protect the earth s surface from ultraviolet radiation. However, at elevated concentrations, ground-level ozone can irritate the respiratory system, reduce lung function, aggravate asthma, increase people s susceptibility to respiratory illnesses such as pneumonia and bronchitis, and cause permanent lung damage. Children, active adults, and people with respiratory diseases are particularly sensitive to ozone. Emissions Data and Sources Emissions of ozone are not reported because ozone is not normally emitted directly into the air. Instead, it is created when ozone precursors such as nitrogen oxides (NO x ) and volatile organic compounds (VOCs) react in a hot stagnant atmosphere. Since heat and sunlight are needed for ozone to be produced, elevated levels of ozone in Minnesota are normally seen on very hot summer afternoons. Ozone precursors come from a variety of sources. NO x can form when fuels are burned at high temperatures. The major NO x sources are combustion processes from automobiles and power plants. VOCs are emitted from a variety of sources, including industrial sources, motor vehicles and consumer products. NO x and VOCs are also emitted by naturally occurring sources such as soil and vegetation. See the Nitrogen Oxides and Volatile Organic Compounds sections of this report for more information regarding 2004 emissions of ozone precursors. References/Web Links For more information on ozone, see the following web sites:

23 Nitrogen Oxides Nitrogen oxides (NO x ) is the generic term for a group of highly reactive gases, all of which contain nitrogen and oxygen in varying amounts. The two primary constituents are nitric oxide (NO) and nitrogen dioxide (NO 2 ). NO is a colorless, odorless gas that is readily oxidized in the atmosphere to NO 2. NO 2 exists as a brown gas that gives photochemical smog its yellowish-brown color. NO x is reported because NO and NO 2 continuously cycle between the two species. NO x form when fuel is burned at high temperatures. NO is the principal oxide of nitrogen produced in combustion processes. NO x contributes to a wide range of human health effects. NO 2 can irritate the lungs and lower resistance to respiratory infection (such as influenza). More importantly, NO x are a major precursor both to ozone and to particulate matter (PM). As discussed in the ozone and PM sections of this report, exposure to these pollutants is associated with serious adverse health effects. High NO x concentrations also have environmental impacts. Deposition of nitrogen can lead to fertilization, eutrophication, or acidification of terrestrial, wetland and aquatic systems. This can result in changes in species number and composition such as the reduction of fish and shellfish populations. In addition, nitrous oxide (N 2 O), another component of NO x, is a greenhouse gas that contributes to global warming. Emissions Data and Sources The MPCA estimate for statewide emissions of NO x in 2002 is 483,628 tons. The figure below shows sources of 2004 NO x emissions. Sources of Nitrogen Oxide Emissions in Minnesota, 2004 Non-road Sources 21% Point 31% On-road Vehicles 35% Area 13% Point source data is from the 2004 Emissions Inventory. All other data is from the 2002 Emissions Inventory. 17

24 The majority of NO x emissions come from the transportation sector, which consists of on-road vehicles and non-road sources. On-road vehicles contribute 35 percent of total statewide NO x emissions, while non-road sources contribute 21 percent of total NO x emissions. Gasoline engines contribute the majority of emissions from the transportation sector. Thirty-one percent of NO x emissions come from point sources, primarily from the utility and mining sectors. Area sources are responsible for the remaining 13 percent of NO x emissions. Residential and small industrial and commercial combustion makes up the majority of area source emissions. Trends Point sources contribute 31 percent of the NO x emissions in the state. In Minnesota, NO x emission estimates from point sources have stayed relatively constant since 2000 with some fluctuation between years. The biggest changes have been in the mining sector. Mining emissions vary annually depending on the demand for taconite pellets. The kilns used to bake the pellets burn natural gas, which results in NO x emissions. Emissions of NO X were relatively flat between 2003 and Utilities and refineries had slightly decreased emissions while the other sectors slightly increased their NO X emissions. Nitrogen Oxide Point Source Emission Trends by Sector in Minnesota, Tons Manufacturing Utilities Mining Refineries Pulp & Paper Other References/Web Links For more information on nitrogen oxides, see the following web site: 18

25 Volatile Organic Compounds Volatile organic compounds (VOCs) are compounds containing the elements carbon and hydrogen that exist in the atmosphere primarily as gases because of their low vapor pressure. VOCs are defined in federal rules as chemicals that participate in forming ozone. Therefore, only gaseous hydrocarbons that are photochemically reactive and participate in the chemical and physical atmospheric reactions that form ozone and other photochemical oxidants are considered VOCs. Many VOCs are also air toxics and can have harmful effects on human health and the environment. However, VOCs are regulated as a criteria pollutant because they are precursors to ozone. See the sections on ozone and air toxics for related human health and environmental effects. Emissions Data and Sources The MPCA estimate for statewide emissions of VOCs in 2004 is 367,175 tons. VOCs are emitted from a variety of sources: including industrial sources, motor vehicles, consumer products and natural sources such as soils and vegetation. The figure below shows only manmade Minnesota sources of VOCs in Sources of VOC Emissions in Minnesota, 2004 Non-Road Sources 23% On-Road Vehicles 25% Area 45% Products Usage 11% Gas stations 17% Agricultural Pesticide Use 10% Industrial Surface Coating 8% Other 31% Point Sources 7 % Residential Wood Burning 23% Point source data is from the 2004 Emissions Inventory. All other data is from the 2002 Emissions Inventory. A little less than half of the emissions come from the transportation sector, which consists of on-road vehicles and non-road sources. Twenty-five percent of emissions come from on-road vehicles and 23 percent come from non-road sources. Non-road sources include recreational equipment, pleasure boats, and lawn and garden equipment as well as other agricultural and commercial equipment. Area sources contribute 45 percent of VOC emissions, primarily from residential wood burning, gas stations, products usage, agricultural pesticide use and industrial surface coating. The final seven percent of emissions come from point sources such as the manufacturing and pulp and paper operations. 19

26 Trends Point sources contribute seven percent of the VOC emissions in the state. VOC point source emission estimates gradually decreased in Minnesota between 2000 and Emissions increased slightly in Increases in manufacturing VOC emissions were partially offset by decreases in the pulp and paper and refineries sectors. Most of the refinery decreases were due to VOC abatement measures undertaken by Flint Hills Resources. Volatile Organic Compound Point Source Emission Trends by Sector in Minnesota, Tons Manufacturing Utilities Mining Refineries Pulp & Paper Other References/Web Links For more information on volatile organic compounds, see the sections on ozone and air toxics. 20

27 Carbon Monoxide Carbon monoxide (CO) is a colorless and odorless toxic gas formed in high concentrations when carbon in fuels is not burned completely. CO enters the bloodstream and reduces the delivery of oxygen to the body s organs and tissues. The health threat from CO is most serious for those who suffer from cardiovascular disease. At higher concentrations it also affects healthy individuals. Exposure to elevated CO levels is associated with impaired visual perception, work capacity, manual dexterity, learning ability and performance of complex tasks. Prolonged exposure to high levels can lead to death. At concentrations commonly found in the ambient air, CO does not appear to have adverse effects on plants, wildlife or materials. However, CO is oxidized to form carbon dioxide (CO 2 ), a contributor to global warming. Emissions Data and Sources The MPCA estimate for statewide emissions of CO in 2004 is 2,125,861 tons. The figure below shows sources of 2004 CO emissions. Sources of Carbon Monoxide Emissions in Minnesota, 2004 Non-road Sources 22% Point 1% Area 15% Point source data is from the 2004 Emissions Inventory. All other data is from the 2002 Emissions Inventory. On-road Vehicles 62% The majority of CO emissions come from the transportation sector, which consists of on-road vehicles and non-road sources. On-road vehicles contribute 62 percent of total statewide CO emissions, while non-road sources contribute 22 percent of total CO emissions. Non-road emissions come primarily from gasoline consumption by lawn and garden, recreational and commercial equipment. 21

28 The remaining 16 percent of emissions come from point and area sources. Area source emissions are primarily from prescribed burning, residential wood burning, forest fires and waste disposal through open burning. Major point source contributors to CO emissions are from the manufacturing and utility sectors. Trends Point sources contribute only 1 percent to the total Minnesota CO emissions. The CO values have been generally flat or decreasing except for high refinery values in This increase was primarily from Marathon Ashland refinery. Normally, the refinery runs its FCC catalyst regenerator in full burn mode, meaning in excess oxygen. In 2002, the refinery's FCC catalyst regenerator ran in both full and partial burn mode, which resulted in higher emissions estimates. The emission estimates returned to normal in 2003 and Emissions of CO from point sources were relatively flat between 2003 and 2004 with a small decrease from utilities and pulp and paper and a small increase in the manufacturing sector. Carbon Monoxide Point Source Emission Trends by Sector in Minnesota, Tons Manufacturing Utilities Mining Refineries Pulp & Paper Other References/Web Links For more information on carbon monoxide, see the following web site: 22

29 Sulfur Dioxide Sulfur dioxide (SO 2 ) belongs to the family of sulfur oxide gases. It is a colorless gas that can be detected by taste and odor at concentrations as low as 0.3 ppm. Sulfur oxide gases are formed when fuel containing sulfur (mainly coal and oil) is burned and during metal smelting and other industrial processes. SO 2 reacts with other chemicals in the air to form tiny sulfate particles. In fact, sulfate aerosols make up the largest single component of fine particulate matter. It is difficult to distinguish between health effects due to SO 2 exposure and those due to fine particulate exposure. The major health effects of concern associated with exposures to high concentrations of SO 2, sulfate aerosols and fine particles include impaired breathing, respiratory illness, alterations in the lung s defenses, aggravation of existing respiratory and cardiovascular disease, and mortality. Children, asthmatics and the elderly may be particularly sensitive. SO 2 also causes significant environmental damage. SO 2 reacts with other substances in the air to form acids, which fall to earth as rain, fog, snow, or dry particles. Acid rain damages forests and crops, changes the makeup of soil, and makes lakes and streams acidic and unsuitable for fish. Continued exposure changes the number and variety of plants and animals in an ecosystem. In addition, SO 2 accelerates the decay of buildings and monuments and is a major cause of reduced visibility due to haze in Minnesota. Emissions Data and Sources The MPCA estimate for statewide emissions of SO 2 in 2004 is 161,179 tons. The figure below shows sources of 2004 SO 2 emissions. Sources of Sulfur Dioxide Emissions in Minnesota, 2004 Non-road Sources On-road Vehicles 6% 2% Area 10% Point source data is from the 2004 Emissions Inventory. All other data is from the 2002 Emissions Inventory. Point 82% 23

30 More than 80 percent of SO 2 emissions come from point sources. Electric utilities burning coal emit the majority of SO 2 attributed to point sources. Non-road sources emit 6 percent of SO 2. Non-road source emissions come primarily from agricultural equipment, marine vessels, trains and construction and mining equipment. On-road vehicles contribute 2 percent of the emissions. These emissions are divided between gasoline-powered cars, trucks and motorcycles, and diesel vehicles. The remaining 10 percent of area emissions of SO 2 result from fuel combustion by small industrial and commercial facilities and residences. Trends Point sources contribute 82 percent to the total state SO 2 emissions. Emissions from point sources have remained relatively constant since Coal-burning utilities are the greatest emitters of SO 2. Total SO 2 estimated emissions decreased slightly between 2003 and 2004 with emissions from the utilities, pulp and paper and refinery sectors decreasing slightly and emissions from the mining and manufacturing sectors increasing slightly. Sulfur Dioxide Point Source Emission Trends by Sector in Minnesota, Tons Manufacturing Utilities Mining Refineries Pulp & Paper Other References/Web Links For more information on sulfur dioxide, see the following web site: 24

31 Lead Lead (Pb) is a metal found naturally in the environment as well as in manufactured products. In the past, the major sources of lead emissions were motor vehicles and industrial sources. Since lead in gasoline was phased out, air emissions and ambient air concentrations have decreased dramatically. Currently, metals processing (lead and other metals smelters) and aircraft using leaded fuel are the primary sources of lead emissions. Lead causes damage to organs such as the kidneys and liver and may lead to high blood pressure and increased heart disease. In addition, exposure to lead may contribute to osteoporosis and reproductive disorders. Most importantly, lead exposure causes brain and nerve damage to fetuses and young children, resulting in seizures, behavioral disorders, memory problems, mood changes, learning deficits and lowered IQ. Elevated lead levels are also detrimental to animals and to the environment. Wild and domestic animals experience the same kind of effects as people exposed to lead. Elevated levels of lead in the water can cause reproductive damage in some aquatic life and cause blood and neurological changes in fish. Emissions Data and Sources The MPCA estimate for statewide emissions of lead in 2002 is 35 tons. The total mass of lead emitted is much less than the other criteria pollutants. However, it takes only a small amount of lead to cause serious and permanent health problems. Therefore, even relatively low lead emissions are a concern. The figure below shows sources of 2004 lead emissions. Sources of Lead Emissions in Minnesota, 2004 Non-road Sources 33% (primarily airplanes using leaded fuels) Area 4% Point 63% Point source data is from the 2004 Emissions Inventory. All other data is from the 2002 Emissions Inventory. 25

32 Non-road sources (primarily airplanes using leaded fuels) contribute 33 percent of Minnesota s lead emissions. Point sources such as utilities and metal processing (including lead and other metal smelters) add an additional 63 percent of lead to the environment. Area sources contribute the final 4 percent of lead emissions. Area source lead emissions result from auto body refinishing, tank cleaning and fuel combustion. Trends Point sources contribute 63 percent of the total state lead emissions. In Minnesota, estimated lead emissions from point sources have decreased since All sector emissions decreased or remained relatively constant between 2003 and Lead Point Source Emission Trends by Sector in Minnesota, Tons Manufacturing Utilities Mining Refineries Pulp & Paper Other References/Web Links For more information on lead, see the following web sites:

33 Carbon Dioxide Carbon dioxide is a gas that is primarily formed from the combustion of fossil fuels such as oil, gas, and coal. It is the major greenhouse gas that contributes to warming of the earth s atmosphere. The earth s greenhouse effect is a natural phenomenon that helps regulate the temperature of our planet. Many greenhouse gases occur naturally, but fossil fuel burning and other human activities are adding gases to the natural mix at an accelerated rate. Emissions Data and Sources The estimate for statewide emissions of carbon dioxide in 2004 is 113 million short tons. The pie chart below shows the breakdown of carbon dioxide emissions from fossil fuel burning by sector. The majority of the carbon dioxide emissions come from the electric utility (36 percent) and transportation (36 percent) sectors. The remaining 28 percent of the emissions come from fossil fuel combustion in the industrial, commercial, residential and agriculture sectors. Sources of Carbon Dioxide Emissions from Fossil Fuel Burning in Minnesota, 2004 Agriculture 2% Commercial 6% Residential 9% Industrial 11% Electric Utilities 36% Transportation 36% 27

34 Trends Carbon dioxide emissions from fossil fuel burning in Minnesota have remained relatively flat from 2002 to Emissions from electric power generation declined by about 2 million tons between 2003 and 2004, but most of that decline was offset by increases in other sectors. Carbon Dioxide Emission Trends from Fossil Fuel Burning in Minnesota, ,000, ,000,000 Tons 80,000,000 60,000,000 40,000,000 Electric utilities Transportation Industrial Residential Commercial Agriculture 20,000,

35 Mercury Mercury contamination of fish is a well-documented problem in Minnesota. The Minnesota Department of Health advises people to restrict their consumption of fish due to mercury from virtually every lake tested. Nearly all more than 95 percent of the mercury in Minnesota lakes and rivers comes from the atmosphere. Consequently, the data presented here only include atmospheric releases. Emissions Data and Sources Mercury emitted to the atmosphere due to human activities is divided by the MPCA into three categories: (1) Emissions resulting from energy production, (2) emissions due to the use and disposal of mercury in products, and (3) emissions due to taconite processing. Sources of Atmospheric Mercury Deposition to Minnesota Minnesota Mercury Emissions 2005 Natural Emissions 30% Regional Emissions 40% Global Emissions 30% Minnesota Mercury Emissions (about 10% of all deposition) Energy Production (mostly coal) 58% Product Disposal 22% Taconite Processing 20% Because mercury vapor can be transported long distances by the atmosphere, most of Minnesota s emissions are deposited in other states and countries, and Minnesota receives their emissions. Minnesota emits about as much mercury as the state receives, and about 90 percent of Minnesota s emissions are carried by the wind out of state. MPCA staff estimates that only about 10 percent of mercury deposition in Minnesota is the result of emissions originating within the state. MPCA staff estimates that the remaining 90 percent of the deposition is due to three roughly equal sources: 30 percent from human-generated sources in the rest of North America, 30 percent from human sources in the rest of the world, and 30 percent naturally cycling mercury. 29